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One of the world's first civilizations began in the area between the Tigris and Euphrates Rivers known as Mesopotamia(modern Irag) where much of the fertile land was under cultivation by 4500 .. Sumer, in southern Mesopotamia, was dominated by eight major cities, including the city of Uruk, which had 50,000 inhabitants by 3000 .. ut the irrigation that nourished Mesopotamian fields carried a hidden risk. Groundwater in miarid regions usually contains a lot of dissolved salt. Where the water table is near the ground surface, as it is in river valleys and deltas, groundwater is moved up into the soil where it evaporates, leaving the salt behind in the ground. When evaporation rates are high. sustained irrigation can generate enough salt to eventually poison crops. While irrigation dramatically increas agricultural output, turning sunbaked floodplains into lush fields can sacrifice long-term crop yields for short-term harvests.
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Preventing the buildup of salt in miarid soils requires either irrigating in moderation or periodically leaving fields fallow(unplanted). In Mesopotam, centuries of high productivity fro
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m irrigated land led to incread population density. which fueled demand for more intensive irrigation. Eventually, enough salt crystallized in the soil that further increas in agricultural production were not enough to feed the growing population.
The key problem for Sumerian agriculture was that the timing of river runoff did not coincide with the growing ason for crops. Flow in the Tigris and Euphrates peaked in the spring, when the rivers filled with snowmelt from the mountains to the north. ischarge was lowest in the late summer and early fall, when new crops needed water the most Intensive agriculture required storing water through soaring summer temperatures. lot of the water applied to the fields simply evaporated, pushing that much more salt into the soil.
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bubble什么意思Salinization was not the only hazard facing early agricultural societies. Keeping the irrigation ditches from becoming blocked by silt(mud) chief concern as extensive erosion from upland farming in the rmenian hills poured dirt into the Tigris and Euphrates Rivers. onquered peoples were put to work pulling mud from the all-important ditches. Sacked an
d rebuilt repeatedly, abylon was finally abandoned only when its fields became too difficult to water. Thousands of years later, piles of silt more than thirty feet high still line ancient irrigation ditches. On average, silt pouring out of the rivers into the Persian Gulf has created over a hundred feet of new land a year since Sumerian time. The ruins of the city of Ur. a once thriving aport. now stand hundred and fifty miles inland.
补发英文blowjob是什么意思s Sumer prospered, fields lay fallow for shorter periods becau of the growing demand for food. y one estimate almost two-thirds of the thirty five thousand square miles of arable land (land suitable for farming) in Mesopotamia were irrigated when the population peaked at around twenty million. The combination of a high load of dissolved salt in irrigation water, high temperatures during the irrigation ason, and increasingly intensive cultivation pumped ever more salt into the soil.
Temple records from the Sumerian city-states inadvertently recorded agricultural deterioration as salt gradually poisoned the ground. Wheat, one of the major Sumerian crops is quite nsitive to the concentration of salt in the soil. The earliest harvest records,
dating from about 3000 .., report equal amounts of wheat and barley in the region Overtime, the proportion of wheat recorded in Sumerian harvests fell and the proportion of barley ro. round 2500 .., wheat accounted for less than a fifth of the harvest. fter another five hundred years, wheat no longer grew in southern Mesopotamia.
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Wheat production ended not long after all the region's arable land came under production. Previously, Sumerians irrigated new land to offt shrinking harvests from salty fields Once there was no new land to cultivate, Sumerian crop yields fell precipitously becau increasing salinization meant that each year fewer crops could be grown on the shrinking amount of land that remained in production y 2000 .., crop yields were down by half. lay tablets tell of the earth turning white in places as the rising layer of salt reached the surface.
mementocos是什么意思1.One of the world's first civilizations began in the area between the Tigris and Euphrates Rivers known as Mesopotamia(modern Irag) where much of the fertile land was under cultivation by 4500 .. Sumer, in southern Mesopotamia, was dominated by eight major citiblame是什么意思
es, including the city of Uruk, which had 50,000 inhabitants by 3000 .. ut the irrigation that nourished Mesopotamian fields carried a hidden risk. Groundwater in miarid regions usually contains a lot of dissolved salt. Where the water table is near the ground surface, as it is in river valleys and deltas, groundwater is moved up into the soil where it evaporates, leaving the salt behind in the ground. When evaporation rates are high. sustained irrigation can generate enough salt to eventually poison crops. While irrigation dramatically increas agricultural output, turning sunbaked floodplains into lush fields can sacrifice long-term crop yields for short-term harvests.
